In general, a mobile terminal is configured to perform various functions. For example, these various functions include video and voice call communications, capturing still or moving images using a camera, storing audio data or voice and images, reproducing music file through a speaker system, and displaying image or video. Some mobile terminals include additional functions such as games and also function as multimedia players.
Moreover, recently, mobile terminals are configured to output video or television programs by receiving broadcast or multicast signals.
Various attempts have been made to implement enhanced functions of the mobile terminal not only by structural improvements, but also by hardware or software improvements. For example, a touch input function of the mobile terminal allows a user to conveniently operate the mobile terminal by using a touch screen. Recently, the touch input function is considered as an important function of the mobile terminal along with a simple input method with User Interface (UI).
Generally, an IP (Internet Protocol) multimedia system provides a PTT (Push-to-talk) over Cellular (PoC) service which is a Session Initiation Protocol (SIP)-based voice service and an Instant Messaging (IM) service which is a text-based service. The PoC service indicates a service for creating and managing a session by using an SIP on the basis of a PoC server and transmitting media, such as voice, video, images and files, through a Real-time Transport Protocol (RTP). The IM service indicates a service for inserting text into a body of an SIP message and transmitting the text through a PoC server or an additional IM server.
The IM service, which is a service for real-time communication, such as chatting or telephony, is frequently used to transmit simple messages, such as memos, files, and data, to users who are in an online status on the Internet or IP in real-time. Once a user transmits a message, the message is immediately output to a screen of a party receiving the message. Accordingly, the IM service allows a message to be transmitted or received in real-time on a wired or wireless network and also allows to immediately check whether the message has been received or not.
In order to use the IM service, each subscriber is required to install an IM program at a communication device, such as computer or mobile terminal, and to register a buddy list consisting of contact-permitted parties or friends. Once the user starts a conversation with another party, one session is created and conversation content is transmitted through the created session.
Accordingly, if the user conducts conversations with a plurality of parties in multiple sessions, a plurality of conversation windows corresponding to the number of the multiple sessions are created on a screen of the mobile terminal such that the user can engage in conversation with a desired party among the plurality of parties by individually selecting one of the plurality of conversation windows on which the desired party is displayed. This will cause the user inconvenience and the UI (User Interface) function of the mobile terminal may become limited due to display of the plurality of conversation windows on the limited space of the screen.
The IM (Instant Messaging) service is a technique for implementing a messenger function in a mobile terminal. However, the conventional IM service has problems when performed in the mobile terminal.
If the user is engaged in conversation with a plurality of parties at the same time while using an IM service, a plurality of conversation windows corresponding to the number of the plurality of parties are created on the screen of the mobile terminal. Thus, the user needs to switch between each of the plurality of conversation windows to engage in conversation with a particular one of the plurality of parties by individually selecting one of the conversation windows on a small screen of the mobile terminal.
Therefore, there is a need for improving the above mentioned problem with regard to performing a plurality of IM conversation sessions or opening a plurality of conversation window corresponding to the plurality of IM conversation sessions in a limited space of the mobile terminal.